DE 10 2013 018 249 A1 discloses a piston of the type in question for an internal combustion engine, having a piston head and a piston skirt, wherein the piston skirt has box walls, which lie opposite one another and have boss bores, and skirt walls, which lie opposite one another and have running surfaces. Arranged in the lower region of the piston is a cover element, which has an aperture for the passage of a connecting rod. To enable this cover element to be fastened reliably on the piston, it has two mutually opposite longitudinal sides and two mutually opposite free ends, wherein grooves, in which the free ends of the cover element are accommodated under spring preload, are provided in the lower region of the skirt walls.
AT 001919 U1 likewise discloses a piston which has a retaining plate, between which and a piston top a space is formed into which there opens an outlet opening and wherein an opening for a return flow of oil is provided in the retaining plate. The intention is thereby both to enable reliable lubrication of a small end of a connecting rod and to achieve uniform cooling.
Cover elements for pistons have already been known for a long time, especially in the case of relatively small pistons, since they make it possible to eliminate expensive production steps for the production of cooling passages with the aid of salt cores.
Moreover, this enables the piston to be made thinner and therefore lighter in a top and in a ring region since there is no need to provide space for the cooling passage, which in each case has to be separated both from the internal chamber and from the combustion chamber and from the rings at least by minimum wall thicknesses. In general, however, spray cooling is less efficient than a cooling passage carrying a flow within the piston since the oil usually comes into contact with the piston only once or twice for a brief period of time and is heated less intensely during this process. For this reason, significantly more oil is required to cool the pistons to dissipate a predefined quantity of heat, requiring additional power from the oil pump and thereby increasing fuel consumption.
Another disadvantage with the spray-cooled pistons with cover elements that are known from the prior art is that, with these pistons, only a certain region of the piston is efficiently cooled but other regions are not cooled at all.